The rigid nature of inorganic semiconducting substrates confines the application of solar cells based on such semiconductors to flat surfaces. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVCs), which are flexible, have the potential to supplant such devices, at least for installation on flexible and/or non-planar surfaces, but such flexible solar cell devices are seldom comparable in durability or efficiency to their rigid counterparts. Consequently, the optimization of flexible device stability and power conversion efficiency (PCE) are the objects of considerable current research.
High-power piezoelectric nanogenerators (PNGs) have been extensively studied in recent years, and constitute an emerging technology. These devices are typically fabricated from rigid ceramic materials, such as bismuth ferrite (BiFeO3, “BFO”) (D. Lee, T. W. Noh, Phil. Trans. R. Soc. A (2012) 370:4944-4957). Lead zirconate titanate (Pb[ZrxTi1-x]O3, “PZT”) is another promising candidate with a very high piezoelectric coefficient, which has recently been formed into flexible devices on plastic substrates (K.-I. Park et al., Adv. Mater. (2014), 26:2514-2520.) Flexible piezoelectric architectures are attracting attention for their practicality, and for the potential to match or exceed their rigid counterparts in conversion efficiency.
Hybrid photovoltaic/piezoelectric energy-harvesting filaments could be woven into textiles or integrated directly within clothing to provide adaptable, portable, and autonomous electricity from both human locomotion and solar radiation. Wind power could be harvested from sails, flags, and highway and advertising signage. Large-scale devices could serve as overhead power lines capable of harvesting energy from solar radiation and from mechanical strain induced by rain and wind. The devices, either alone or serving as trickle chargers for batteries, could power a variety of commercial and biomedical electronics such as cellular phones, prostheses, pacemakers, and hearing aids. The versatility of this technology promises additional applications in automotive, military, robotics, aerospace, and other fields, but the limitations on rigid structures, noted above, are an impediment to advances in the field. Accordingly, there is an ongoing need for such hybrid devices having increased flexibility and improved efficiencies and operating lifetimes.